Smarter %postun script to preserve /var/rancid on upgrade and removal

Of course I find a major bug right after submitting a PR! Sorry about that.

Previosly the %postun would delete /var/rancid even when performing
an update. Not good! Now it will move /var/rancid to /var/rancid.rpmsave
and save any existing /var/rancid.rpmsave to /var/rancid.rpmsave.[date].

Update %global commit